Multi-function vibrating actuator devices (referred to hereafter simply as “devices” as necessary) that generate both a bodily-sensible vibration and a ring tone in a single device are generally known, as means of notification of incoming calls in terminal equipment represented by portable telephones.
This sort of multi-function vibrating actuator device, as exemplified by the inner-magnet type shown in FIG. 24, comprises a housing 1 that is substantially cylindrical and open at both ends, a magnetic circuit 2 that includes a pole piece 2a and a yoke 2b fastened to a magnet 2c and separated by a gap G1 that functions as the magnetic gap, a diaphragm 4 that is fastened atop a voice coil 3, and suspensions 5, 5′ that supports the magnetic circuit 2.
Within this device, the diaphragm 4 is mounted so as to cover one open end of the housing 1, such that the voice coil 3 is located within the magnetic gap G1 and the edge of the diaphragm 4 is fixed within one open end of the housing 1. The opening at the other end of the housing 1 is covered by a ring-shaped cover 6 that is fitted into the other open end of the housing 1. The voice coil 3 is electrically connected to terminal fittings 7a (7b) mounted on the outside of the housing 1 by lead wires that run from the diaphragm 4 to the outside of the housing 1.
The suspensions 5, (5′), as shown in FIG. 25 (both are the same shape, so only one suspension is shown), comprise a supporter 5a that is fixed to and supports the magnetic circuit, an outer ring 5b that is mounted inside the housing 1, and three spring arms 5c through 5e that are located at equal distances (separated by 120° in the example shown) and extend in the same direction from the outer edge of the supporter 5a (circumferential, in the example shown) to connect the supporter 5a and the outer ring 5b (see, for example, Patent Document 1).
The suspensions 5, 5′ are mounted by fitting them inside the housing 1 so that the supporter 5a supports the magnetic circuit 2. In greater detail, spacer rings 8a, 8b are located in the spaces between the supporters 5a and the outer rings 5b of the suspensions 5, 5′, and the supporter 5a that is fitted to the outside of the yoke 2b is held in place by a stopper ring 9; the outer ring 5b is held in place by the cover 6. In this way the magnetic circuit 2 is assembled so that it is supported and able to vibrate by flexing the spring arms 5c through 5e. 
This multi-function vibrating actuator device is mounted in portable terminal equipment, and when a communication signal is received from elsewhere, a low-frequency electrical signal is impressed on the voice coil 3 and, by means of the electromagnetic action in the vicinity of the magnetic gap G1, the magnetic circuit 2 vibrates and that vibration is transmitted outwards. The user of the terminal equipment is made aware of the vibration as a bodily-sensible vibration, and the user is thus notified of the incoming call. On the other hand, if the incoming call causes a high frequency electrical signal to be impressed on the voice coil 3, the electromagnetic action in the vicinity of the same magnetic gap G1 causes the diaphragm 4 to vibrate and that vibration generates a ring tone or other sound, and the user is thus notified of the incoming call.
In conventional multi-function vibrating actuator devices, a large clearance G2′ is maintained between the inner surface of the housing 1 and the outer surface of the yoke 2b in order to allow the flexing of the spring arms 5c through 5e. Accordingly, together with the vibration of the magnetic circuit 2, the air within the device moves freely within the device through the clearance G2, and so there is almost no resistance from the internal air to the vibration characteristics of the magnetic circuit 2. Therefore, the vibration of the magnetic circuit 2 quickly starts up at resonant frequencies, and the bodily-sensible vibration characteristics are limited to a narrow frequency range that yields the desired vibration acceleration.
For example, when the acceleration necessary for bodily-sensible vibration is at least A0 [G] as shown in FIG. 26, the range of frequencies at which that acceleration can be obtained is the narrow frequency range fa [Hz]. And as the maximum acceleration A1 [G] is approached, there is maximum bodily-sensible vibration at that point, or in other words it is a point of resonance, but as soon as the frequency reaches or exceeds f1 [Hz], the acceleration falls sharply, and above f3 [Hz] the acceleration falls below A0 [G] and the necessary acceleration is unavailable.
In the frequency range below f1 [Hz], on the other hand, the drop in acceleration is comparatively less steep, but there is still a drop, and at frequencies less than f4 [Hz] the acceleration is less than A0 [G]. Therefore, if the frequency varies even slightly from the point of resonance, there will be a sharp drop in the amount of bodily-sensible vibration.
For that reason, in the event that the manufacturing process causes a scattering of vibration characteristics from one device to the next, or that there are variations in the environment of use of the terminal equipment in which the devices are mounted, it will be difficult to set the point of resonance and the frequency range within which the desired vibration acceleration can be obtained will be narrow, as described above, and so the point of resonance can easily fall outside that frequency range.
Further, when there is a blow to the outer case of the portable terminal equipment in which the multi-function vibrating actuator device is mounted, the vibration is conveyed to the multi-function vibrating actuator device, and the magnetic circuit vibrates. In conventional multi-function vibrating actuator devices, the magnetic circuit is supported by suspensions having the structure described above, and so the vibration characteristics of the magnetic circuit, as measured through the outer case, follow the curve shown in FIG. 27. The vertical axis of FIG. 27 indicates the amplitude of vibration of the magnetic circuit, and the horizontal axis shows the passage of time.
According to these vibration characteristics, if vibration is conveyed to the device when the portable terminal equipment in which the multi-function vibrating actuator device is mounted is awaiting an incoming call, or in other words, when the multi-function vibrating actuator device is not in operation, the magnetic circuit will vibrate for some time and cause vibration of the air, which will produce a strange noise like a plucked bowstring.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-1215